Умножим обе части на 20, получим
4(4x + 3)^2 - 5(5 - x)^2 = 20
4(16x^2 + 24x + 9) - 5(x^2 - 10x + 25) = 20
64x^2 + 96x + 36 - 5x^2 + 50x - 125 - 20 = 0
59x^2 + 146x - 109 = 0
D = 47040;
√D = 56√15
x₁ =( - 146 + 56√15)/(2*59) = ( - 73 + 28√15)/59;
x₂ =( - 146 - 56√15)/(2*59) = ( - 73 - 28√15)/59;